Andrew G. Sparks

Multiple task assignments for cooperating uninhabited aerial vehicles using genetic algorithms

A problem of assigning cooperating uninhabited aerial vehicles to perform multiple tasks on multiple targets is posed as a new combinatorial optimization problem. A genetic algorithm for solving such a problem is proposed. The algorithm allows us to efficiently solve this NP-hard problem that has prohibitive computational complexity for classical combinatorial optimization methods. It also allows us to take into account the unique requirements of the scenario such as task precedence and coordination, timing constraints, and trajectory limitations. A matrix representation of the genetic algorithm chromosomes simplifies the encoding process and the application of the genetic operators. The performance of the algorithm is compared to that of deterministic branch and bound search and stochastic random search methods. Monte Carlo simulations demonstrate the viability of the genetic algorithm by showing that it consistently and quickly provides good feasible solutions. This makes the real time implementation for high-dimensional problems feasible.

Robust multivariable flight control

Manual flight control system design for fighter aircraft is one of the most demanding problems in automatic control. Fighter Aircraft dynamics generally have highly coupled uncertain and nonlinear dynamics. Multivariable control design techniques offer a solution to this problem. Robust Multivariable Flight Control provides the background, theory and examples for full envelope manual flight control system design. It gives a versatile framework for the application of advanced multivariable control theory to aircraft control problems. Two design case studies are presented for the manual flight control of lateral/directional axes of the VISTA-F-16 test vehicle and an F-18 trust vectoring system. They demonstrate the interplay between theory and the physical features of the systems.

Modeling, identification, and feedback control of noise in an acoustic duct

Although active noise control has been a subject of interest for over 50 years, it has become feasible only with recent technological advances. This paper formulates the problem of noise control in a one-dimensional acoustic duct in a form that lends itself to the application of feedback control theory. In contrast to most of the literature on the subject which uses feedforward techniques, a feedback approach is used. Inconsistencies that appear in previous feedback control models are rectified, controllers are designed using precompensated linear quadratic Gaussian (LQG) synthesis, and experimental verification of the control designs is presented. The experimental results show a reduction of about 5-12 dB over a frequency range from 150-350 Hz.

Spacecraft formation flying: dynamics and control

A concept of a distributed array of small, low-cost, cooperative, and highly coordinated microspacecraft is vigorously being pursued for several future space missions. Implementation of the distributed coordinated spacecraft concept will require tight control of the relative distances and phases between the participating spacecraft. We review nonlinear and linear spacecraft relative position modeling techniques. In addition, we develop a mathematically rigorous control design framework for linear control of spacecraft relative position dynamics with guaranteed closed-loop stability. Finally, illustrative numerical simulations are provided to demonstrate the efficacy of the proposed approach.

An overview of rotating stall and surge control for axial flow compressors

Modeling and control for axial flow compression systems have received great attention in recent years. The objectives are to suppress rotating stall and surge, to extend the stable operating range of the compressor system, and to enlarge domains of attraction of stable equilibria using feedback control methods. The success of this research field will significantly improve compressor performance and thus future aeroengine performance. This paper surveys the research literature and summarizes the major developments in this active research field, focusing on the modeling and control perspectives to rotating stall and surge for axial flow compressors.

Bifurcation Stabilization with Local Output Feedback

Local output feedback stabilization with smooth nonlinear controllers is studied for parameterized nonlinear systems for which the linearized system possesses either a simple zero eigenvalue or a pair of imaginary eigenvalues and the bifurcated solution is unstable at the critical value of the parameter. It is assumed that the unstable mode corresponding to the critical eigenvalue of the linearized system is not linearly controllable. Results are established for bifurcation stabilization using output feedback where the critical mode can be either linearly observable or linearly unobservable. The stabilizability conditions are characterized in explicit forms that can be used to synthesize stabilizing controllers. The results obtained in this paper are applied to rotating stall control for axial flow compressors as an application example.

Design of a LQR controller of reduced inputs for multiple spacecraft formation flying

Regarding multiple spacecraft formation flying, the observation is made that control thrust need only be applied coplanar to the local horizon to achieve complete controllability of a two-satellite formation. Without the need for zenith-nadir (radial) thrust, simplifications and reduction of the weight of the propulsion system may be accomplished. The authors focus on the validation of this radial-excluding control system on its own merits, and in comparison to a related system which does provide thrust parallel to the orbital radius. Simulations are performed using commercial ODE solvers to propagate the Keplerian dynamics of a controlled satellite, relative to an uncontrolled, leader satellite. The conclusion is drawn that, despite the exclusion of the radial thrust axis, the remaining control thrust available still provides enough control to design a gain matrix of adequate performance using linear-quadratic regulator (LQR) techniques.

Satellite formation keeping control in the presence of gravity perturbations

The performance of linear control laws for satellite formation keeping in the presence of gravity perturbations is considered. Control using a linear quadratic regulator to minimize the error between the actual and desired relative satellite motion is assessed for its ability to maintain a particular formation geometry in the presence of the Earth oblateness gravity perturbation. The desired formation geometry is based on the solution to the linear, unperturbed relative motion equations. Specifically, a formation of satellites is chosen whose projected motion onto the Earths tangential plane is a one kilometer circle. It is shown that the linear control laws maintain the formation within error bounds in the presence of gravity perturbations. Furthermore, simulations provide estimates of the maneuvering propellant required to maintain such a formation, providing a baseline for future studies involving formations based on less taxing desired trajectories and more carefully chosen control strategies.

Geometry and control of satellite formations

Satellite formations based on the solutions to Hills equations have relatively simple geometric shapes. This paper shows that all such formations around a leader satellite in a circular orbit are determined by the intersection of a plane and an elliptic cylinder of eccentricity /spl radic/3/2. In a moving coordinate system fixed to the leader. The parametric equations of these formations lead to a method of deploying the satellites in a formation. These equations are also essential in the design of tracking controls to herd the member satellites into a desired formation after the initial deployment, and to nudge them back into formation as soon as they start drifting due to perturbations. The adjustable parameters in these equations are key to the reconfiguration of formations from one plane to another, enabling us to aim and re-aim a satellite array which is used as sensing device.

Stable task load balancing strategies for Cooperative control of networked autonomous air vehicles

We introduce a mathematical model for the study of cooperative control problems for multiple autonomous air vehicles (AAVs) connected via a communication network. We propose a cooperative control strategy based on task-load balancing that seeks to ensure that no vehicle is underutilized and we show how to characterize task-load balancing as a stability property. Then, using Lyapunov stability analysis, we provide conditions under which task-load balancing is achieved even in the presence of communication delays. Finally, we investigate performance properties of the cooperative controller using Monte Carlo simulations. This shows the benefits of cooperation and the effects of network delays and communication topology on performance